[Dovecot] Corrupted index cache files

I see these errors more often than I'd like from Dovecot-1.1.2 on Mac
OS X 10.5.4 (names and numbers elided):

Corrupted index cache file %s: Corrupted virtual size for uid=%d: %d ! = %d Corrupted index cache file %s: Broken virtual size for mail UID %d Corrupted index cache file %s: used_file_size too large

How bad are these? What should I look for to find out why they happen?

Other details: File system is HFS+ Mail store is maildir Hardware is Intel (Mac Pro)

Thanks.